The present invention relates to an electronic circuit module having an improved mechanism for electrically connecting top and bottom metal covers to the ground plane of a printed circuit board housed within the module, and includes provisions for connecting the ground plane of the printed circuit board to a reference ground potential of a host device. The preferred embodiment of the invention provides these improved features in an electronic circuit module conforming to the PCMCIA standard for electronic devices, however, it should be clear to one of ordinary skill in the art that the present invention is well adapted for use with other electronic modules not conforming to the PCMCIA standard but nevertheless having metal covers requiring grounding, and modules further requiring the connection of an internal printed circuit board ground plane to a reference ground potential of a host device.
Printed circuit board modules are well known in the art. Generally, such devices are provided to increase the capacity or add additional functionality to a host device. Common applications include supplying additional memory, modems, or pluggable software modules for personal computers. The PCMCIA standard was developed in order to maintain interconnectability between various manufacturer's devices. The standard provides uniform external package specifications and connector requirements so that various electronic circuit modules can be interchangeable with various model small computers. When assembled, a PCMCIA card comprises a narrow rectangular card like package having a 68 pin connector integrally provided with one of the short transverse edges of the PCMCIA package. This standard configuration allows the PCMCIA card to slide into a narrow predefined slot within a personal computer, or other host device, where the 68 pin connector engages a similarly configured mating connector located at the end of the slot. The connection between the host device and the PCMCIA card allows the additional electronic circuitry housed within the PCMCIA card to interact with the host device.
PCMCIA packages and the printed circuit boards housed within them are usually manufactured separately. Generally, the printed circuit board is manufactured first, having the 68 pin connector soldered to an edge of the board. Then the PCMCIA package is assembled around the printed circuit board, or alternatively, the printed circuit board is inserted into a pre-assembled PCMCIA package through an opening in the connector side of the package. In either case, the completed assembly forms a sealed module with the 68 pin connector being integrally formed within one edge of the module.
In most cases, PCMCIA cards consist of a plastic rectangular frame which acts to support the printed circuit board and the 68 pin connector. Top and bottom covers, usually made of metal, attach to both sides of the frame forming an internal cavity for housing the printed circuit board. A variety of methods for attaching the metal covers to the plastic frames are known in the art. Some PCMCIA cards are made having a single frame and metal covers that snap fit over the frame. Others are made having two piece frames where each half of the frame is injection molded directly to the top and bottom covers, and the two frame portions are welded together around the printed circuit board. Depending in the design, the printed circuit board can be placed in the frame before the module is assembled, or it can be inserted into the internal cavity between the two covers after the frame and covers have been assembled. In either case, a standard PCMCIA package results having metal top and bottom covers secured over a plastic frame. The plastic frame supports the printed circuit board and secures the 68 pin connector within a transverse edge of the package.
The electronic device housed within the PCMCIA package will be exchanging signals with the host device, therefore, it is necessary that the signals generated by the PCMCIA device share the same reference ground potential as the signals generated by the host device. To ensure this, the ground plane of the printed circuit board must be connected to the reference ground potential supplied by the host device. The reference ground of the host device can be brought to the printed circuit board via ground pins included within the 68 pin connector, the ground pins can then be soldered to contact pads connected to the ground plane of the printed circuit board. It is also desirable to protect the PCMCIA device against the deleterious effects of electromagnetic interference (EMI). This can be accomplished by grounding the metal covers of the PCMCIA package to provide a degree of EMI shielding.
A number of methods have been employed for grounding the metal covers of PCMCIA cards, most involving the use of ground clips which clip onto the printed circuit board then extend perpendicularly away from the board to contact the covers. The use of ground clips requires the formation of ground pads on the surfaces of the printed circuit board, and the ground pads are then connected to the ground plane of the printed circuit board. In one design, ground clips are attached to ground pads prior to the assembly of the PCMCIA package. Using this approach, the ground clips can be soldered to the ground pads to ensure a secure path to ground. In another prior art design, ground clips are inserted over the frame after the printed circuit board has been placed within the frame. The metal covers snap over the frame, thereby contacting the ground clips. This latter design has the advantage of being easier to assemble, but provides a less solid path to ground. Furthermore, the external ground clip design cannot be used with those PCMCIA packages having the frame portions injection molded directly to the metal covers. In a final prior are design, tabs are formed integrally with the metal covers. When the covers are placed over the frame, the tabs engage the ground pads on the printed circuit board.
A major problem with existing methods of grounding the covers of PCMCIA cards is the necessity of forming ground pads on the surface of the printed circuit board. To meet the requirements of the PCMCIA standard, an electronic device must fit on the surface of a compact printed circuit board capable of being mounted within a PCMCIA size frame. Because of the size limitations of the PCMCIA standard, space on the printed circuit board is at a premium. Providing ground pads on the surface of the board takes up valuable real estate on the printed circuit board which could be used more productively by adding additional circuitry and functionality to the device.
An additional problem with existing designs is that they require an additional step in the manufacturing process. Prior to the final assembly of the PCMCIA package, the ground clips must be inserted onto the printed circuit board to engage the ground pads. In some cases, the clips must then be soldered to the pads. The insertion of ground clips onto the printed circuit board adds time and cost to the assembly process, raising the cost of the final product.
In light of the problems with the prior art, a need exists for an electronic circuit module having an improved mechanism for grounding the metal covers of the module to the ground plane of a printed circuit board inserted therein. The improved mechanism should accomplish this task without requiring the formation of ground pads on the printed circuit board, or any other structures which consume real estate on the printed circuit board. Furthermore, such an improved mechanism should perform its grounding function without requiring any additional assembly steps. In other words, the grounding of the metal covers of the PCMCIA package should be accomplished by the act of assembling the package itself, with no additional steps required. Finally, in addition to grounding the metal covers, the improved grounding mechanism should also electrically connect the metal covers and the ground plane of the printed circuit board to a designated ground pin of the module connector so that the ground reference of the host device can be coupled to the ground plane of the printed circuit board.